You have a new website. New sites tend to rank high from the very beginning, but in about a month (there's no common time span though) rankings drop.

Is your website new?

It sometimes happens than you rank for keywords you never targeted don't bother about it much.

Still, please make sure that you use a variety of anchor texts when building links - not just russian bride / russian brides but a variety of other options (the more the better).

Also I advise you to start a project for your website with Rank Tracker entering your site's url and your two main keywords.

First look for longer keyword suggestions.

Then check your rankings for each of these keywords as well as let the tool count KEI (= keyword efficiency index). KEI will show you if the keyword is worth chasing after.

Also check visits brought by each keyword last month (get your Google Analytics login info to make that possible) + estimated number of visitors each keyword can potentially bring you if you rank #1 for it.

If unexpected keywords are appearing in content keywords report that might mean that your site is hacked and malware added. if you have comments etc enable in your website it could be due to spam comments as well. Getting unrelated keywords in that report is clearly a problem.
However I notice that the list of keywords showing in the report are somewhat related to brides. So the report might be correct and you are optimizing for the wrong keywords.